This invention relates to electron beam cold hearth furnaces and, more particularly, to a new and improved electron beam furnace having a high capacity.
In electron beam cold hearth refining of metals, a solid skull of the metal being refined is formed on the surface of the cold hearth. Moreover, during the refining and casting operation, spattered drops of molten metal solidify on the walls and other interior surfaces of the hearth. Consequently, whenever there is a change in the composition of the material being refined, the furnace must be shut down, cooled and opened to permit thorough cleaning of the interior surfaces so as to avoid contamination of the next batch of material to be refined. The time required to effectuate such changes includes not only the time involved in cooling, removing the skull and cleaning the furnace and then re-establishing the necessary high vacuum for electron beam operation, but also the time involved in outgassing the interior of the furnace, which usually requires many hours.
Furthermore, even if the same product is being refined continuously, it is necessary to change condensate collection screens within the furnace periodically to avoid build-up of condensate which can catch fire during venting of the furnace for a maintenance cycle and thereby damage furnace components.
Because of these considerations, the maximum production time which can be expected with conventional electron beam cold hearth furnaces is no more than about 40%, the balance of the time being required for maintenance work, set-up and start-up for each new refining run and handling of material being supplied to or removed from the furnace. In view of the high cost of electron beam furnaces, it would be economically advantageous to increase the production time for such furnaces.